Agglomeration and cluster formation of microscacle particles and droplets in highly loaded turbulent gas flows

• Applicant: Professor Dr.-Ing. Michael Breuer
• Subject Area: Fluid Mechanics
• Term: from 2012 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 215541820

The objective of the project is to model, simulate and analyze the dynamic process of particle agglomeration in turbulent, highly loadeddisperse multiphase flows. In the first project period significant progress was made based on a four-way coupled Euler-Lagrange approach relying on the large-eddy simulation technique for the description of complex turbulent flows and a simultaneous particle tracking scheme for the disperse phase. On the basis of a deterministic treatment of the particle-particle collisions two new agglomeration models and a wall adhesion model were developed. These were first validated based on various test cases and for a wide parameter range and then successfully applied for the analysis of the agglomeration processes within turbulent flows of highly loaded fluids. Thereby new insights into the physical relationships concerning the agglomeration of particles and their most important influencing factors as well as the feedback of the agglomerates on the turbulent flow field was gained.The objective of the second project period is to incorporate the effect of breakage of agglomerates which for simplification purposeswas not taken into account yet, but plays a significant role for the description of the entire process. In technical applications thegrowth of agglomerates is the result of the interplay between agglomeration and breakage of the agglomerates leading to thecharacteristic particle size distribution. That in turn decisively determines significant processes such as the separation for example infilters or cyclones, the dosing of pharmaceuticals or the reaction rates in chemical reactors. Therefore, the description of bothphenomena is indispensable for a realistic simulation of highly loaded turbulent two-phase flows.From the list of the three most important mechanisms of breakage particular attention will be paid to the break-up of agglomerates dueto fluid-induced forces. Deviating from the state-of-the-art in the literature (break-up of massless and solely small agglomerates, DNSand mostly homogeneous isotropic turbulence) the fluid-induced break-up of agglomerates with mass (inertia) will be modeled and lateranalyzed, where a clear distinction is made between small agglomerates (d < Kolmogorov length l_k) which may break up due to viscous forces and large agglomerates (d > l_k) for which the inertia forces are responsible for a possible breakage. Due to their practical relevance wall-bounded shear flows are in the focus of interest. Besides the development of a modern sustainable simulation concept, the main goal is to improve the physical understanding of the build-up of agglomerates and their potential breakage. In addition to the fluid-induced breakage of agglomerates the break-up due to particle-wall and particle-particle collisions will be included in the modeling concept, the simulation and the final analysis. At the end an overall concept for practically relevant applications will beavailable.

• DFG Programme: Research Grants